This invention relates to a method of insulating multi-conductor, medium-voltage electrical power cables at locations where the cable insulation has been removed, and, in particular, to insulating a joint between such cables and to the resulting joint. Medium voltage is used herein to specify voltages in the range of about 1 to about 36 kilovolts (kV).
It has long been known to insulate a joint between multi-conductor cables with a cured resin system. Typical AC multi-conductor cables contain three conductors at the same voltage but in different phases. Conventionally, a joint between such cables is enclosed by a metal or plastic joint box. Resin is poured through vents in the box and allowed to cure. The cured resin insulates the conductors from each other and from the joint box. To prevent the conductors of the cable from contacting each other, a solid separator can be placed between the conductors. It has been found that the resin, which is typically at an elevated temperature when it is poured into the joint box, tends to solidify when it touches the cold conductors. This can result in voids between the conductors and between the conductors and spacer, if one is used. This method of insulating joints is cumbersome and time consuming.
Another method of insulating joints is to use a heat shrinkable enclosure such as that disclosed in U.S. Pat. No. 4,383,131. This technique has been used with single core cables and with multi-conductor cable. When used with multi-conductor cables, each of the conductors of the cable is generally separately insulated and shielded. A heat shrinkable enclosure is then installed over the joint. Enclosing and insulating a joint by this method requires numerous steps to install the various insulating and shielding components.
This invention relates to a method of using a heat-shrinkable enclosure to provide insulation between the conductors of a joint between multi-conductor, medium-voltage power cables, which method provides the advantages of a resin filled system without the inconvenience and other disadvantages typically associated with such systems, while maintaining the advantages of ease of installation of heat-shrinkable systems without requiring individual insulation and shielding of each conductor.